In the constant frequency method of recording (CFR) on a magnetic disk, the disk's angular velocity (RPM) is held constant, and data is supplied to a recording head at a constant binary data rate (bits per second or bps). This method of recording produces a linear data density (bits per linear track unit length) that varies inversely with track radius. That is, linear recording density is greatest at the disk's inner track. The recording capability of a given recording head and magnetic media can therefore be maximized only at the inner track.
Various methods have been used to more fully utilize the head/media recording capability.
One prior art method is to decrease the disk's RPM as the head moves radially outward of the disk, so that a constant surface speed exists between the head and the disk with increased track diameter. When data is recorded at a constant data rate, constant density recording (CDR) results. As a result, utilization of the head/media recording capability can be maximized.
This method is difficult to practice, however, due to the high inertia of a rotating disk, particularly where the disk is a hard disk, and the resulting difficulty in rapidly changing the disk's RPM in a random access environment.
Another prior art method involves providing bands of recording tracks, and changing of the data rate for each recording band. In this method, each band's data rate or frequency is chosen such that at the inner track of each band the head/media capability is maximized. A disadvantage of this method is that different data channel characteristics must be provided for each of the different frequency bands.
While such prior art methods increase utilization of the head/media to some extent, complex disk drive means must be provided to quickly change the disk's RPM, or multi frequency data channels must be provided.
The present invention practices CFR (i.e. constant data rate and disk RPM recording), by making use of a magnetic recording head whose generally linear gap is skewed, in a continuously increasing manner, to the disk radius at the location of each disk track, from the inner to the outer track, and wherein the disk's radial track density is caused to increase as the written track widths become narrower.
The present invention provides a major portion of the increase in capacity produced by a variable RPM CDR system. However, the present invention does not require a change in disk RPM.
The present invention produces a capacity increase comparable to a 3 band frequency system. In practice, using the well known ferrite heads, the advantages of a multi-frequency system is degraded by the head's failure to optimally perform at the different frequencies. The variable track density system of the invention is not degraded in this manner, and thus provides comparable benefits, while not requiring multiple frequency data channels.
U.S. Pat. No. 4,388,655 is of interest relative the concept of a skewed head gap. This patent is directed to a arrangement for improving the density and fidelity of video recording. In accomplishing the objects of this patent, it is taught that the recording head(s) be moved along a path that is non-radial of the disk. Curved paths and linear paths are suggested for head movement. However, in all cases the teachings of this patent are (1) that the skew of the head gap to the disk radius should preferably remain constant, and (2) when the head(s) move along a linear path, a spiral track is written whose track-width becomes wider as the head(s) is moved from the inner disk diameter to the outer disk diameter.
As will be apparent, these two requirements are opposite to the requirements of the present invention, and do not provide for reduced track width and reduced track spacing, from the disk's inner track to the disk's outer track.
Skewed recording, also called azimuth recording, is known in the video recording arts, where adjacent tracks are recorded with heads of opposite gap skew. U.S. Pat. No. 4,479,156 is an example. In this type of recording, the gap skew remains constant for each head across all corresponding tracks.
A feature of the present invention provides a unique air bearing head slider having a generally parallelogram shape, wherein the slider's rails extend more nearly perpendicular to disk radii, and wherein the skewed head gap is generally parallel to the slider's leading/trailing edges. This feature allows use of the invention in the art of rigid disks, where non-contact recording is necessary.
U.S. Pat. No. 4,486,798 discloses an air bearing head of the conventional rectangular shape, where the slider's rails and the head gap are skewed to the disk's tangential velocity vector line. In the device of this patent, the head moves along a disk radius. Thus, the gap skew remains constant from track to track.
The concept of a rectangular shaped air bearing slider head whose slider contour facilitates flying with a slider skew angle is described in the publication IEEE Transactions on Magnetics, Vol. Mag-22, NO.5, September 1986, in an article entitled "A UNIFORM FLYING HEIGHT ROTARY ACTUATOR AIR BEARING SLIDER", by J. W. White. This head provides small angle side tapers on the flying rails of a conventional rectangular shaped slider head. These side tapers are similar to the head's leading edge tapers, and they allow a partially lateral direction of flight of the slider relative a disk radius.